Expand and combine like terms. $(7b^5-4b)(7b^5+4b)=$
Answer: We can expand this expression like any product of two binomials. However, this expression has a special form that makes it easier to expand. This is the "difference of squares" form (where $P$ and $Q$ can be any monomial): $(P+Q)(P-Q)=P^2-Q^2$ $\begin{aligned} &\phantom{=}(7b^5-4b)(7b^5+4b) \\\\ &=\left(7b^5\right)^2-\left(4b\right)^2 \\\\ &=49b^{10}-16b^2 \end{aligned}$